Drafting instrument



P 26, 1967 G. s. DOLGORUKOV 3,343,266

DRAFTING INSTRUMENT 2 Sheets-Sheet 1 Filed Jan. 19, 1967 Ill 1 I N VENTOR.

Sept. 26, 1967 as. DOLGO'RUKOV 3,343,266

DRAFTING INSTRUMENT I Filed Jan. 19, v1967 2 Sheets-Sheet 2 I NVEN TOR.

v SEW United, States Patent 3,343,266 DRAFTING INSTRUMENT Gregory S.Dolgorukov, Ferndale, Mich. (407 Fisher Bldg., Detroit, Mich. 48202)Filed Jan. 19, 1967, Ser. No. 621,377 Claims. (Cl. 3375) ABSTRACT OF THEDISCLOSURE A T-square having unseparably connected blade and headelements wherein the head element is provided with two recesses underthe blade. The recesses extend beyond the guiding surfaces of the bladeand are disposed so that the guiding surface of the blade can be recutand the cutter of the cutting machine will not contact the head.

This invention relates to drafting or geometric instruments, and moreparticularly to an improved T-square, and a method and apparatus formanufacturing or repairing the same. The present application is acontinuation-inpart of my co-pending applications, Ser. No. 347,070filed on Feb. 18, 1964 now abandoned, and Ser. No. 477,074 filed July16, 1965, now abandoned for Drafting Instrument.

Great difliculties have been experienced within the last decade withT-squares, and not only little progress has been made in providingfurther improvements in T- squares, but T-squares made within the lastdecade in accordance with conventional designs proved to be greatlyinferior to similar T-squares made even as far back as 25 years ago. Toappreciate fully the difficulty of the problem which those skilled inthe art are now facing, one has to appreciate that T-squares have beenproceeding in their progress along a path similar to that of draftingtriangles. This path or direction of progress is from being aninstrument made of wood to an instrument made completely of transparentplastic. In the initial stage of their development drafting triangleswere made of especially selected wood, such as pear wood. In the nextstage, the triangle became an instrument made of wood with plastic linedguiding surfaces, and finally it became an instrument made completely oftransparent plastic. At the present time both wood triangles andtriangles made of wood with plastic lined edges have completelydisappeared in this country, although their use is still remembered bythe older draftsmen. However, wooden drafting triangles are still in usein some foreign countries, particularly Germany.

The development of T-squares, while definitely proceeding along the samelines, has been much slower, and T- squares made completely of wood,while not used in any appreciable number by professional draftsmen, arestill in use, such as in schools in classes for beginners. Forprofessional work and advance school work a T-square with plastic linedguiding surfaces is now in wide use.

However, development of a T-square made completely of plastic materialhas met so many difficulties and problems that there has been a generalunderstanding in this art that difficulties of making a T-squarecompletely out of plastic material by cutting or milling operations fromcast and annealed sheets of such material as acrylic plastic are soserious that a practical T-square of such nature is still somewhere inthe distant future.

It should be understood, however, that there have been attempts ofmaking T-squares out of transparent plastic by injection moldingoperations. Such operations involve melting plastic material to liquidstate and injecting it into metal molds under pressure, wherein it israpidly cooled for removal from the mold. While molded plastic items ofvarious character are in wide use, they possess various disadvantagesand advantages, their particular advantage being found in ease and lowcost of manufacturmg of intricate shapes, and their main disadvantage inshort life, due to breakage mainly because of brittleness of thematerial.

The shape of T-squares is not particularly intricate, and, therefore,the above advantages is of no great value. On the other hand,brittleness of the material, resulting from its rapid cooling in themolds, proved to be a very serious disadvantage. Even a small nick onthe sharp edge of the squared guiding surface of a T-square isexceedingly annoying, and in professional drafting often causes a T-square to be discarded. Even in school use, presence of several suchnicks may require discarding the T-square or finding a way to removesuch nicks. Use of so-called extruded strips for T-square arms connectedto molded heads proved to have the same disadvantage of brittleness andease of cracking because of internal stresses caused by the rapidcooling of the plastic material in the process of extrusion. Inaddition, both molded and extruded T- square blades or arms have Wavysurfaces distorting the image underneath and causing eye strain in use.On the other hand, wooden T-squares with plastic lined surfaces whichproved to be exceedingly durable and practical during the past 30 or 40years proved, within the last decade, to have a tendency ofdisintegrating rather rapidly.

One of the difliculties in making T-squares entirely out of plasticmaterial was found to be in connecting the head to the blade. Whilesmall T-squares, such as 9" in size (length of the blade), could bemolded as a single piece, i.e., integrally with the head, to do so witha T- square even of such size as 24" is impractical. Connection of aplastic blade to a plastic or wooden head with the aid of screws provedto be objectionable. Drilling holes through the blade for passage of thescrews weakens the blade at such places and originates cracks.Therefore, breakage of the blades through screw holes proved to be verycommon. Nevertheless, some of such T-squares are on the market. Togetherwith wooden T-squares and T- squares with plastic lined edges orsurfaces, such T- squares also possess the advantage of a possibility ofseparating the blade and the arm should it be necessary to refinish theedges of the arm because of the occurrence of nicks in the sharp edgesof its guiding surfaces after a certain period of use. With the use ofcast and annealed acrylic plastic sheets with optically fiat surfaces asamaterial for T-square blades, and use of construction such as disclosedin my various co-pending applications and patents, origination of nicksdue to internal stresses and extension of minute cracks produced bycutters has greatly decreased, and the permanent joint between the headand the blade completely eliminated loosening of such joint.Nevertheless, some serious difficulties still remain. It has beenbrought out that no matter how durable and otherwise advantageous such aT-square may be and no matter how valuable is the advantage of having anonloosening and non-separating joint between the head and the blade ofsuch a T-square from a functional viewpoint, such joint has a greatdisadvantage as not permitting separation of the blade from the head forrefinishing the guiding edge surfaces of the T-square should, for anyreason whatsoever, any nicks develop on the guiding edges of suchT-squares, i.e. on the sharp edges of the squared longitudinal guidingsurfaces thereof.

Such objection is based on the fact that the guiding surfaces of aT-square with a permanently attached head cannot be refinished on astandard machine such as a shaper or a jointer because of theinterference of the head. In fact, after the appearance of all solidacrylic T-squares with permanent joints, in some instancesspecifications of quantity purchasers of T-squares required that theblade be separable from the head for the purposes of refinishing theguiding surfaces, it being presumed that guiding surfaces of a T-squarecannot be refinished unless the head of the T-square is first separatedtherefrom. It is believed that such a condition virtually blockedfurther progress and development of T-squares made wholly of plasticmaterials and making further improvements in their constructions, suchas elimination of screws or other types of separable joints which arenot fully suited for plastic T-squares.

An additional disadvantage of T-squares having their blades made ofplastic material rather than of a wooden plank with plastic lined edgesis that in case of a fall, particularly on hard cement floors, the freeends of the blades break off in substantial pieces or chip very easily.While the disadvantage of chipping of the free ends of T- squares hasbeen greatly reduced by the construction disclosed in my said co-pendingapplication, seemingly inexplicable breakage of large pieces at the freeends of T-square blades made even of the best acrylic material, such ascast and annealed sheet, continued.

One of the objects of the present invention is to provide an improvedmethod and apparatus whereby guiding surfaces of a T-square havingunseparable joint between its head and blade can be smoothened orrefinished in a simple and easy manner and without the necessity ofremoval of the head or its separation from the blade.

Another object of the present invention is to provide an improvedapparatus of the character specified in the preceding paragraph which isin the form of an attachment useable in combination with simple standardmachines such as drill presses or routers, and with the attachmentitself being of such a simple character'that it can be easilymanufactured or made in a school shop and as a teaching project.

A further object of the present invention is to provide an improvedmethod and apparatus for refinishing guiding surfaces of T-squareshaving unseparable joints between their heads and blades, with the aidof which the guiding surfaces can be refinished with removal of aminimum amount of material from such surfaces, and without cutting anyamount of material from the heads.

A still further object of the present invention is to provide animproved T-square having a construction which makes use of the methodand apparatus disclosed in the present application particularlyadvantageous and not affecting the strength or appearance of theT-square.

A still further object of the present invention is to provide animproved method and apparatus whereby T- squares, both of unitaryconstructions as well as those with separable heads, which are found tohave their blades secured or connected to their heads with guidingsurfaces thereof not in strictly perpendicular relationship to the headcan be corrected, and the guiding edges of the blades recut in strictperpendicular relationship to the guiding surface of the head.

A still further object of the present invention is to provide animproved T-square having its blade made entirely of plastic material andin which breakage of relatively large pieces at the free end of theblade is greatly reduced and virtually eliminated.

A further object of the present invention is to provide a T-square ofunitary construction made of a plastic material, which T-square isparticularly advantageous for having its guiding surfaces refinished bythe method and with the aid of the apparatus disclosed in the presentapplication, and in which the head is not affected in its appearance orstrength by a condition that would otherwise be caused when it isattempted to refinish the guiding surfaces of the blade at the place ofits juncture with the head, and in which the area of the joint betweenthe blade and the head affecting the strength of such joint is notreduced in the process of refinishing guiding edges, and the appearanceof the entire T-square is not noticeably aifected by the refinishing ofits guiding surfaces.

A still further object of the present invention is to provide animproved T-square having an all-plastic blade in which the weakness ofthe free ends of the blade noted in such T-squares is eliminated andpossibility of breakage of such ends in falling on a hard fioor isgreatly reduced.

Further objects and advantages of this invention will be apparent fromthe following description and appended claims, reference being had tothe accompanying drawings forming a part of this specification, whereinlike reference characters designated corresponding parts in the severalviews.

FIG. 1 is a view showing an improved T-square of an all-plasticconstruction with a non-separating joint between the head and the blade,and embodying the present invention.

FIG. 2 is a fragmentary sectional view taken in the direction of thearrows on the section plane passed through the line 2-2 of FIG. 1.

FIG. 3 is an elevational view on a larger scale of the head of theT-square of FIG. 1.

FIG. 4 is an end view taken on the T-square head of FIG. 3 with theobserver looking from right to left on the guiding edge of the head.

FIG. 5 is a fragmentary perspective view showing the middle portion ofthe T-square head of FIGS. 3 and 4.

FIG. 6 is a top or plane view of the improved guiding surfacerefinishing apparatus embodying the present invention, with the guidingsurfaces of the blade of such T-square being located therein forrefinishing in such a manner that the refinished surfaces are also madeperpendicular with respect to the guiding surface of the T-square head.

FIG. 7 is a view similar in part to FIG. 6 but showing a construction ofthe same general nature as in FIG. 6 but having modified locating meanswhereby the edges are refinished parallel to their respective originalsurfaces and without truing such surfaces to ensure theirperpendicularity with respect to the guiding surface of the head. Aportion of the device is broken off to decrease the total length of thedrawing.

FIG. 8 is an end view with the observer looking on the construction ofFIG. 7 from right to left.

FIG. 9 is a right-hand end view of the construction of FIG. 6.

FIG. 10 is a view showing on an enlarged scale the T-square of FIG. 1,with the middle portion of the blade thereof being broken away forcompactness of the drawmg.

FIG. 11 is a view showing on an enlarged scale the portion of theT-square encircled in FIG. 10 by the circle C.

FIG. 12 is a view similar in part to FIG. 11 but showing the cutter inits terminal position in the head recess after blade-trimming operationhas been completed.

FIG. 13 is a view similar in part to FIG. 12 but showing the refinishedblade at its place of juncture with the head, with the cutter removed.

It is to be understood that the invention is not limited in itsapplication to the details of construction and arrangement of partsillustrated in the accompanying drawings, since the invention is capableof other embodiments and of being practiced or carried out in variousways. Also, it is to be understood that the phraseology and terminologyemployed herein is for the purpose of description and not of limitation.

In the drawings there is shown by way of example a T-square embodyingthe present invention. In addition to having the functional andstructural advantages disclosed in this application, the T-squaredisclosed herein is particularly advantageous for having its guidingsurfaces refinished with the aid of the method and apparatus disclosedbelow. Referring particularly to FIGS. 1-5, the T-square illustratedtherein comprises a head generally designated by the numeral 10 and ablade generally designated by the numeral 11 and connected together atthe joint area 12 in any suitable manner such, for instance, asdisclosed in my Patent No. 3,103,071.

In the top portion of the head at the guiding surface thereof 14 thereare provided two semi-circular recesses 15 extending downwardlyapproximately onequarter to one-half of the thickness of the head. Thesharp top and bottom edges of the head along the straight guidingsurface 14 thereof may be beveled as indicated at 16 and 17. While alongthe entire lower edge and portions of the upper edge outwardly of therecesses 15 such bevel may be a straight angular bevel as indicated, onI the top edge between the recesses 15 the bevel is of a modified crosssection. As is shown in FIG. 5, between the recesses 15 there isprovided a groove 18 having crosssection in the form of a quartercircle. It may also be in the form of an angle with rounded corner. Suchform increases its holding capacity for foreign matter that may tend tobe retained under the blade at its place of juncture with the head,prevents tight wedging in of foreign particles between the blade and thehead at said location, and adds to the advantages in manufacturing thehead and particularly in producing the joint.

It is desirable to make the head somewhat wider than has been doneheretofore in order to increase the length of the end of the bladeconnected to the head and thus to increase the area of the joint and itsstrength.

The free end of the blade 11 has rounded corners and is beveled not onlyat its end edges but also around its rounded corners to eliminatechipping, as disclosed in my said co-pending applications.

I have discovered that breakage of large pieces from the free ends ofthe T-square blades made of plastic material does not result from theproperties of plastic materials as such, even in cases of injectionmolded blades in which the material is rapidly chilled in metal molds.Such breakage results from the provision of the hole in such end as hasbeen customarily done with T-squares for the purpose of hangingT-squares on the wall. With T-squares having blades made of wood, theprovision of such holes did not afiect the strength of the T-square inany appreciable degree. It has been customary to produce such holes bydrilling with the hole being approximately /2-%" in diameter. I havefound that such holes are not suitable for plastic blades and that suchholes have to be either entirely eliminated or their provision has to bedone in a different manner. In accordance with the invention, thediameter of the hole 19, see FIGS. 2 and 10, provided in my improvedT-square is made only A or diameter even in T-squares as large as 36".

Such hole, while unaccustomedly small (even in the smallest T-squaressuch as 11" holes are presently made larger), it is, nevertheless,entirely sufiicient for hanging the T-square on a hook or nail. However,decreasing the diameter of the hole increases the strength of the bladein more respects than has been heretofore appreciated in the :art. Itcan be appreciated by analogy with other situations that providing asmaller hole leaves in the free end of the blade a greatercross-sectional area in the locality of the hole and thus does notreduce the crosssectional area and the strength of the end in the samedegree as a larger hole would.

However, it has not been appreciated heretofore that a much moreimportant result of decreasing the diameter of the hole lies indecreasing the length of its circumfereuce, or the length of the sharpedges of the hole, which, according to my discovery, are the main causeof breakage of the ends of plastic blades. In accordance with theinvention, I increased the durability and strength of the end of myimproved T-square in three main respects: first, by increasing thecross-sectional area of the blade on the plane passed through the endhole, as mentioned; second, by decreasing the length of the hole edgesand the probability of developing the condition explained below; andthird, by removing the strained material at the sharp edges of the hole,in which edges the cracks have already 6 originated or are about tooriginate if any additional stress is imposed thereon. The Walls of thehole including their portions formed by chamfering may be polished toproduce shiny surfaces and blending them into the similarly shinysurfaces of the top and bottom of the blade, thus restoring the surf-acetension interrupted by drilling.

As shown in FIGS. 2 and 10, the sharp edges of the blade at said hole 19both at the top and at the bottom surfaces of the blade are chamfered orrounded for approximately .O30" or more as indicated at 20 in order toremove the material at said edges. I have found that in drilling holesin plastic blades, irrespective of the type of drill used, when theblade is about to break through the bottom of the hole such breakagebeginswith cracking of the material around the periphery of the bottomof the hole. Thereupon, actual breaking of the drill through the plasticsurface takes place by breakage of the plastic and cracking thereof,with such cracking even being audible if carefully listened to. Thecracks so originated, while infinitesimally small at the start are beingonly approximately .010".012" in size and even smaller continue to growinto the body of the blade as time goes on. In the case of suddenadditional stress and strain imposed on the material by the impact of afall, the material cracks at such holes through said cracks, producingthe objectionable condition referred to above.

I have also found that should extreme care be exercised and only verylight pressure exerted on the drill when it is about to break throughthe plastic material at the bottom of the hole, the resulting conditionof the material may be even worse. With very slow and careful feeding ofthe blade, the time of drilling the last portion of the hole is greatlyincreased and the friction of the drill causes heating of the adjacentportion of the material and even melting of such material immediatelyadjacent to the rotating drill. Such heated or molten material rapidlychills when the drill is withdrawn and sets up severe internal stressesin the material at the vicinity of the hole. Such internal stresses mayorigin-ate cracks either within a very short time after completion ofthe drilling operation or may cause their formation later when impactstrain is imposed on such material. By eliminating the affected materialwhere cracks have already originated or are about to originate, I haveproduced a T-square with plastic blades, the ends of which are free frominternal stresses and cracks around the edges of the hole, andeliminated the condition causing the objectionable occurrences referredto above.

As shown in FIG. 10, in addition to eliminating the serious cause ofbreakage by the above-described construction of the hole in the free endof the T-square, I have also reduced to a minimum and virtuallyeliminated the breakage of the free end of the T-squar'e blade usuallyin pieces or flakes at the corners and at the transverse surface formingthe end surface thereof. Such breakage has been plaguing this particulartrade, and virtually each and every T-square made of acrylic plasticshows unsightly evidence of such breakage after a relatively shortperiod of use such as 2-3 years. Such breakage was considered to beunavoidably evil and the usual solution of this difliculty was toreplace the T-square, or the blade if it was removable from the head.

In accordance with the present invention, I eliminate the abovedifficulty in a novel manner and virtually without any additional costby trimming the T-square in a special manner. It is important thatT-square blades should be trimmed to exactly the same length. I attainthis object by trimming the free end of the blade after the blade isassembled to the head. The trimming is done with the T-square locatedwith respect to the cutter by having the guiding surface of the headbearing on the stop means set at a predetermined distance from thetrimming cutter. Instead of usual straight milling cutter, I use agrooved milling cutter with a groove of curvilinear cross section, suchas arcuate and the like, in order to produce convex cross section of thetransverse end surface of the cutter, as shown in FIG. 10. Thus, inaccordance with the invention the trimming operation is also a formingoperation.

After completing such operation, I also trim the corners formed at theintersections of the arcuately convex end surface and the squared sideguiding surfaces of the blade, preferably on a 45 angle, as shown inFIG. 10, and for a distance such as approximately 16 Thus, such cornersalso have convex cross section. After cutting, the convex surfaces maybe sanded and steel wooled, and are buffed on the polishing wheel torestore the luster and therefore the surface tension in such surfaces. Ihave found that the ends of the T-square blades so constructed resistbreakage, even in falls on hard surfaces such as cement floors, to suchan extent as to be unexpected and surprising to those skilled in theart.

It should be understood that refinishing guiding surfaces of T-squareblades may be done for two purposes: first, to eliminate nicks on thesharp edges of such surfaces; and second, to produce trueperpendicularity of the guiding surfaces of the blade, i.e. to make themextend in stricter perpendicularity to the guiding surface of theT-square head.

Accordingly, there are disclosed in the present application two devicesto be used for the purposes of refinishing guiding surfaces of T-squareswithout removing their heads. In the device illustrated in FIGS. 6 and 9the T- square is so located during the refinishing operation that thecutter will finish the surface making it perpendicular to the guidingsurface of the head. On the other hand, in the device of FIGS. 7 and 8the T-square is so located that the cutter will refinish the surfaceparallel to the guiding and the guided surfaces of the device andirrespective of the perpendicularity to the guiding surface of the head.The device of FIGS. 7 and 8 is simpler in its construction, more compactand can be used to advantage where the T-square blade and head areoriginally assembled in proper perpendicularity, and refinishing thesurfaces is done primarily to eliminate nicks or to improve theirStraightness.

It should be understood, of course, that in the device of FIGS. 6 and 9both purposes may be attained simultaneously. In other words, with theuse of the device of FIGS. 6 and 9, while the edge surfaces are beingrefinished to eliminate nicks, the perpendicularity of the guiding edgesurfaces of the T-square head and of the blade may also be corrected andStraightness of the blade edge surfaces improved. In this connection itshould be understood that with the use of the device of FIGS. 6 and 9 itis possible to attain perpendicularity of both the upper and the lowerlongitudinal guiding surfaces of the T-square with respect to theguiding surface of the T-square head. It is not possible to attain suchperpendicularity in the conventional method of manufacturing unless theedge surfaces of the blade are made strictly parallel. Attaining suchparallelism is extremely difficult and doing so while making the bladeis extremely difiicult and costly. Accordingly, the device of FIGS. 6and 9 may be used not only for refinishing guiding or edge surfaces ofT-squares after a period of use but in production of new T-squares. Bydoing so both edges of the T-square so produced could be used in makingthe same drawing.

Referring specifically to FIGS. 6 and 9, the device illustrated thereinis adapted to be used in combination with or as an attachment to anymachine which has a work table and a cutter provided adjacent said tableand rotatable around an axis perpendicular to said table. It ispreferable to have the table extending horizontally and the cutterarranged above the work table perpendicularly to it, i.e. rotatablearound a vertical axis. It is also desirable, but not absolutelynecessary, that the cutter be vertically adjustable, and particularlythat it can be moved down to a certain position, locked in said positionfor cutting, and thereupon raised from said position to be withdrawnfrom the work.

It is of importance that the device disclosed herein can be used inconnection with common standard machines, particularly such machinesthat may be found in any school shop, such as a common drill press or arouter. Furthermore, the device is so constructed that it can be madevery easily in a school shop and also as a teaching project by making anattachment for connection to such machine with the aid of common Cclamps.

In the construction illustrated in FIGS. 6 and 9, the device isillustrated as used in combination with a common drill press having acolumn embracing cylinder 25 and a work table 26. The supporting area ofthe table of such drill press is entirely sufiicient to support thedevice attached to it with the aid of common clamps 27. However, itwould not be sufficient by itself to support the movable part of thedevice. It will be understood, however, that should there be available amachine having a work table of sufiicient area and a cutter 29 asspecified above, the stationary part of the device can be eliminated,and merely a straightedge of metal, wood, or any other suitable materialbe used and secured to such table with the aid of clamps or otherwise.

The stationary or supporting and guiding portion of the device of FIGS.6 and 9 comprises an elongated plate or board 30 having lengthapproximately twice that of the longest T-square intended to berefinished, and width approximately one-and-a-half or two times that ofthe length of the head. This plate may be made of aluminum or othermetal, plywood board or any other suitable material. Along one of thelongitudinal edges or edge surfaces of the plate or board 30 there issecured to it in any suitable manner such as with the aid of screws 31,a straightedge 32 having a guiding surface designated by the numeral 33.Straightness of the guiding surface 33 is important to ensure precisionof the refinishing operation.

The movable part of the device of FIGS. 6 and 9 comprises an elongatedmember, plate or board 35 made of high grade plywood or aluminum andhaving the length substantially equal to the length of the blade of theT- square to be refinished thereon. Along one of the longitudinal edgesurfaces of the board 35 there is provided a straight guided surface 36cooperating with the straight guiding surface 33. As in the case of theguiding surface 33, straightness of the guided surface 36 is alsoimportant and for the same reasons. At the ends of the board or member35 there are provided straight locating surfaces 37 and 38 extendingperpendicularly to the guided surface 36. Straightness andperpendicularity of the surface 36 and of the locating surfaces 37 tnd38 are important.

Fastening means adapted to fix the T-square on the board 35 in itslocated position are exemplified by the clamps 39 provided on said boardand adapted to bear on the blade of the T-square for the purpose ofholding it in place. Any desired number of such clamps may be provided.While tightening such clamps on the blade may be done with the aid ofcommon nuts tightened with the aid of a wrench, I have found thatprovision of wing nuts, Isslich as 40, is sufiicient to ensure properfastening of the ade.

In order to prevent sagging or bending of the blade under pressure ofthe cutter 29, I provide blade-supporting means. In the presentembodiment such blade-supporting means are exemplified by a wooden plankor a metal strip 45 provided with a transverse slot 46 through whichpasses a bolt 47 having thereon a wing nut 48. By virtue of such aconstruction the strip 45 may move bodily transversely of the blade 11and rotatable around the bolt 47. A groove as indicated at 49 in FIG. 9is provided in the board 35 for accommodating the cutter 29 and thus topermit the cutter to be moved downwardly to a position when its lowerextremity is below the lower surface of the blade 11 to ensurerefinishing of the edge through its entire thickness.

For operation, the board 35 may be either removed from the stationarystructure or moved thereon toward the operator for ease of loading, andthe blade 11 of the T-square placed on the board 35 in such a positionthat the upper guiding surface thereof slightly overhangs the supportingedge and extends over the groove 49. Thereupon, the guiding surface 14of the T-square head is pressed against the edge 37 to locate theT-square in the proper position. Thereupon, the amount of overhang ofthe edge to be refinished is checked and adjusted in order to ensure thedesired depth of cut. This may be done by moving the T-square up or downwith the surfaces 37 and 14 remaining in contact until the properposition is determined. It may also be done by loosening one or bothclamps 27, moving the plate 30 to have the guiding surface 33 comecloser or further away from the cutter 29. Thereupon, the plank 45 ismoved against the lower edge surface of the blade 11, permitted toadjust itself to said edge surface and tightened. The clamps 39 are thentight ened against the blade 11, and the T-square is ready forrefinishing.

The board 35 is then placed with its guided edge surface 36 against theguiding edge surface 33 and the free end of the blade 11 in closeproximity but not yet reaching the cutter 29. The operator then takes afirm hold of the board 35 at two convenient places, such as at clamps 39and moves the board 35 from left to right. As soon as the end of theblade 11 touches the cutter 29, the cutter begins to take a cut andcontinues to do so as long as the board 35 is moved. When the head ofthe T-square reaches the stop '50 provided substantially on the line aapassing through the center of the cutter, and to a position indicated inFIG. 6 in light dotted lines, itis stopped in that position. In thisposition of the T-square, the cutter enters into one of the recesses andtherefore completes refinishing of the edge surface right to the line ofits juncture with the head. Because of the provision of the recess 15,no cutting of the head and altering its appearance takes place either atthe bottom or at the sides of the recess 15, see FIGS. 8, l2 and 13.When the board is thus brought to a stop, the cutter is raised or theboard 35 is manipulated to withdraw it away from the cutter withoutraisin-g the same. Thereupon, the win-g nuts 40 are loosened, and theT-square is removed. The cutter 29 should have its diameter smaller thanthat of the recess 15 in order to ensure suflicient clearance. I preferto make recesses 15 to have diameter of /s" and /s" deep, and use acutter, such as common router bit, of A diameter. With suchrelationship, generally illustrated in FIG. 12, it is possible torefinish the blade edge surfaces at least three times without cuttingthe walls of the recesses 15 and thus affecting their appearance, and atthe same time to permit rapid production. However, in school shops useof /s" router bit allowing for larger clearance within the recesses 15,a condition desirable for an apprentice, may be more advantageous.

For refinishing the lower edge surface of the T-square blade, theT-square is turned around and is fixed on the board 35 with the guidingedge surface 14 of the T-square head in contact with the straightlocating edge surface 38, i.e. in the position indicated in FIG. 6 inheavy dotted lines. Tightening of the clamps 39 and of the supportingstrip is made similar to that described above. The board 35 is thenplaced in position with the edge surface 14 of the T-square in contactwith the stop and the cutter 29 is lowered into the recess 15, or theboard 30 is suitably manipulated to bring the cutter 29 into the recess15. Thereupon, the board 30 is moved from left to right with the cutterperforming its edge finishing operation until the .T-square comes intothe position to have its head in the position indicated with dash anddot line in FIG. 6, in which position of the end the free end of theblade begins to move away from the cuter 29, i.e. the edge surface ofthe T-square being refinished through its entire length.

It will be noted that in loading the T-square for the second part of theoperation described above, i.e. refinishing the lower guiding edgesurface of the blade, the supporting strip 45 may be left in itstightened position when unloading the T-square after the firstoperation. However, inasmuch as the width of the blade will then bereduced by the amount of the cut on the upper edge of the blade, aspacer, such as a piece of wire of the thickness equal to the depth ofthe cut may be placed between the blade 11 and the strip 45.

It should be noted that the above specified direction of movements ofthe board 35 with the T-square fixed thereto with respect to the cutter29 are selected for direction of rotation of the cutter as indicated onthe drawing, in order that in cutting the cutter 29 would tend to pressthe work and, therefore, the board 35 against the guiding edge surface33. Should rotation of the cutter be in the opposite direction, thedirection of the movements of the board 35 would have to becorrespondingly changed.

The device illustrated in FIGS. 7 and 8 is intended for refinishing theguiding edge surfaces of the T-square blade without reference to theirperpendicularity to the guiding edge surface of the head. This device issmaller for the same size T-sq-uares to be refinished, is lighter, morecompact and is easier to use. It is advantageous in cases where the headand the blade are originally assembled in proper perpendicularrelationship of their guiding edge surfaces and, therefore, ifrefinishing of the guiding surfaces of the blade is done parallel totheir original guiding surfaces, such perpendicularity is preserved.

Referring specifically to FIGS. 7 and 8, the stationary portion of thedevice comprises a supporting board 60 and a straightedge 61 havingguiding edges, i.e. squared guiding surfaces, 63 provided thereon. Itwill be noted that for reasons which will become clear from furtherexplanation, the construction of the stationary portion of this deviceis substantially the same as that of the stationary portion of theconstruction of FIGS. 6 and 9 except that the board 60 is somewhatnarrower than the board 30 of the device of FIGS. 6 and 9.

The movable portion of the device of FIGS. 7 and 8 comprises a plate orboard 65 having provided thereon a guided edge surface 66 cooperatingwith the guiding edge surface 63. A locating strip 67 having a straightlocating edge surface 68 is permanently secured to the board 65 in sucha manner that when one edge surface of the blade of the T-square isplaced tight against said edge surface 68 the opposite edge of theblade, that is, the blade to be refinished, is exactly parallel to theguided edge surface 66 of the board 65.

It should be noted in this connection that in this particularconstruction the end edge surfaces 69 of the movable board 65 do notserve as locating edges and may merely serve as stops for the T-squarehead in placing it on the board 65. In other words, the guiding edgesurface of the T-square should not be pressed against the end edgesurface 69 of the board 60 but should merely touch it at some point orbe adjacent to it without actually contacting said edge surface 69.Location of the locating strip 67 on the board 65 is also so selectedthat when a blade 11 of a T-square if placed against the locating edgesurface 68, the edge surface of the blade to be refinished will slightlyoverhang the guided edge surface 66 as illustrated, and, therefore, thecutter 29 clears said edge surface 66. A plurality of clamps 70 isprovided on the board 65 to hold the blade 11 in its located position onthe board 65 during the refinishing operation. Tightening of the clamps70 is done with the aid of wing nuts 71.

It shall be understood that with T-squares having blades with edgesurfaces on both sides of the blade being parallel to each other, thelocating edge surface 68 of the strip 67 is disposed parallel to theguided edge surface 66. However, should T-squares having tapering bladesbe intended to be refinished on a device of this nature, the locatingstrip 67 is set to have the locating edge surface 68 make at the sameangle with the guided edge surface 66 as the lower edge surface of theblade makes with the edge surface on the other side of the blade.

I have found that the devices disclosed above may be made of wood withtheir plates or boards being made of plywood, and straight-edges made ofhard wood, such as oak, and made straight on a common Woodworkingmachine such as a jointer. However, should particularly high precisionof operation be required, metal straightedges may be used for edges 32and 61. Also, metal straightedges can be secured to movable boards 35and 65 to provide guided edge surfaces '36 and 66 that are true and wearresistant.

It will be understood that the above disclosed method and apparatus areapplicable with equal success for refinishing guiding surfaces of bladesof T-squares other than those made entirely of plastic material as wellas those having separable joints between the blade and the head. Forinstance, the method and apparatus disclosed herein can be usedsuccessfully and to good advantage on T-squares made entirely of woodand as well as on those having wooden blades with plastic lined edges.Even if the heads of such T-squares are separable, the use of the abovedisclosed method and apparatus may be advantageous as giving additionaladvantages such as simultaneous correction of any lack ofperpendicularity.

Also, the provision of recesses such as 15 on the T- square head is notindispensable for using my method and apparatus thereon, since, in theprocess of refinishing, the cutter will form such recesses. Theadvantage of providing such recesses in advance is that such recessesmay be polished and thus give the T-square head a definite and pleasingappearance which is not altered by the refinishing cutter.

FIG. 13 illustrates the appearance of the place of juncture of the head10 with the blade 11 after the guiding edge surfaces of the blade havebeen refinished. It will be noted from an examination of said figurethat by removing the portion 11;- throughout the entire guiding orworking portion of the guiding edge surface, a rounded step 11s havingradius equal to that of the cutter 29 is formed. Said step 11s isdisposed wholly within the recess 15 and has appearance blending withthat at the recess as an original design. Repeated refinishing of theedges 11 do not affect this condition, but on the contrary may improveit further. Since the'center of the cutter 29 in its terminal positionin the recess 15 lies within said recess, the refinished guiding edgesurface is straight up to and sufficiently far beyond the guiding edgesurface 14 of the head ensuring straightness of the lines drawn from thevery edge surface 14.

Precision of the devices described above may be ensured with respect tothe straightness of the refinished edge surfaces by lining the edges ofthe boards or plates thereof with steel straightedges secured thereto.To ensure perpendicularity of the blade edge surfaces with respect tothe guiding edge surface of the head, the end edge surfaces 37 of theboard may be also lined with a shorter straightedge which is madeadjustable as to its perpendicularity with respect to the edge surface36, such as with the use of a slot-and-screw mechanism. Such anexpedient permits checking perpendicularity of the edge surfaces 36 and37 before starting operation, and enables the operator to correct anymisalinement which might have occurred.

It will be understood that the term surface bond and bounding thesurfaces of the head and the blade refers to constructions in which suchsurfaces are secured together by the use of cements, adhesives, or bythe use of solvents affecting the materials of the head and the blade.In FIGS. 10-13 location of such surfaces is designated by dotting thesame.

It will be also understood that the term guiding edge surface of thehead as well as the term guiding edge surfaces of the blade and the termguiding edge of the straightedge are used in the common manner of theart and designate, in effect, walls, or squared guiding surfaces, witheach of said walls or squared guiding surfaces having a sharp top edgeand a sharp bottom edge defining or forming the boundaries of said wallsurfaces. The term elongated articulated recess is used to designate anelongated recess having ditferent cross-sections along the variousseparate portions of its length. By cross-section of a recess is meantthe cross-section of the removed portion of the material.

In accordance with the invention, the results attainable by theconstruction of the head as illustrated in FIGS. 3-5 may be attained andin some instances enhanced further by cutting, against a suitabletemplate, and in a single operation the reliefs or bevels 17 and 18 aswell as both recesses 15. In such a case such bevels or reliefs, as wellas the recesses will be of the same depth. Also, in the use of thismethod I prefer to have the recesses such as 15 to be of an elongated orrectangular form with well rounded corners. By such an expedient, Ireduced the number of cutting operations from five to only one, whichpresents an important manufacturing advantage.

It should be understood that one of the most important advantages of themethod and construction of the T- square produced thereby is the factthat elimination of concentration of localized stresses in the blade atthe place of juncture with the head is attained Without undercutting andthus weakening the blade by the recesses disposed at the place of thehighest bending moment, and without having such recesses materiallyreduced or completely eliminated together with their stress-reducingadvantage by recutting the side guiding surfaces of the blade. Both ofsuch disadvantages decreasing the effectiveness of the solutionsdisclosed in my Patent No. 3,103,071 have thus been eliminated.

By virtue of the above disclosed construction and meth- 0d, the objectsof the present invention listed above and numerous additional advantagesare attained.

I claim:

1. A method of making a T-square, for such T-square to have a head witha squared guiding surface and a blade having squared side guidingsurfaces and one end unseparably connected to the upper surface of thehead for the life of the T-square and the other end free, and to providefor repeated recutting during the life of the T- square of the sideguiding surfaces of said blade without decreasing their originaleffective guiding length or removal of the blade from the head toeliminate interference thereof with such recutting, said methodcomprising the step of providing the head, prior to its connection tothe blade with two recesses, each of said recesses extending into saidhead from the upper and guiding surfaces thereof and havingsubstantially uniform depths to provide flat bottoms and disposedsubstantially at the places of intersection of the guiding surfaces ofthe blade with the guiding surface of the head, a substantial part ofeach recess underlying the blade and a substantial part of each recessbeing exposed beyond the corresponding guiding surface of the blade,said recess having such configuration and size as to receive therein aside milling cutter in a position normal to the plane of the blade inrecutting of the respective guiding surface to its full original lengthbut without touching any portion of the head.

2. The method defined in claim 1 with said recesses having substantiallysemi-circular configuration.

3. The method defined in claim 1 with recutting of the T-square beingdone by a side milling cutter rotating around an axis normal to theplane of the blade of the T- squareand movable bodily along astraight-line path perpendicular to the guiding surface of the headbetween a respective recess and the end of the blade.

4. The method defined in claim 1 and including additional steps oftransversely cutting the free end of the T-square blade after the sameis permanently connected to the head with a curvilinearly grooved cutterto have the blade brought to precise predetermined length and in thesame operation to make the transverse end surface of the blade convex,and thereupon cutting of the corners formed at the intersections of saidtransverse convex surface with the squared side guiding surfaces alsowith a grooved cutter movable at a predetermined angle to the squaredside guiding surfaces to produce straight corner surfaces of convexcross section.

5. The method defined in claim 1 with recutting of the T-square beingdone in a device comprising a machine having a work table, a verticallydisposed side cutter provided above said table, a guiding straightsurface provided on said table, a plate having a straight guided surfaceadapted to cooperate with said guiding surface as said plate is movedalong said guiding surface, locating means on said plate to align theblade of a T-square to have its surfaces tobe smoothened parallel tosaid guided surface, and fastening means to fix the blade of theT-square in its located position on said plate, means to adjust saidguiding surface with respect to the cutters to determine the depth ofthe smoothening cut, stop means limiting movement of the T-square headtoward the cutter substantially to a position Where refinishing of theguiding surface is completed throughout its entire length.

6. The method defined in claim 5, with recutting of the squared sideguiding surfaces being done in a device made in the form of anattachment to a machine having a flat horizontal work table and avertically disposed side milling cutter provided above said table.

7. A T-square having a head with a squared guiding surface and a bladehaving squared side guiding surfaces, the upper surface of said head andsaid blade being permanently and unseparably connected together for thelife of the T-square, the side guiding surfaces of said blade havingcontinuous straight-line edges at the bottom thereof, two recessesextending into said head from the upper and guiding surfaces thereof andhaving substantially uniform depth and flat bottoms provided on thehead, at the place of intersection of the guiding surface of the headwith the guiding surfaces of the blade,la substantial part of eachrecess underlying said blade and a substantial part of each recess beingexposed beyond the corresponding guidingsurface of said blade, saidrecess having such configuration and size as to receive therein a sidemilling cutter of at least dia. in recutting the respective side guidingsurfaces to their full original length without touching any portion ofthe head, and thus to provide for repeat recutting the side guidingsurfaces without decreasing the original effective length thereof,without forming a step within such length, and without separating thehead from the blade.

8. The T-square defined in claim 7 and including reliefs between the tworecesses as well as between the respective recesses and the ends of theT-square head, both of said recesses and said reliefs having uniformdepth in order to be all cut in a single operation.

9. The T-square defined in claim 7, the free end of the blade havingconvex cross section in its transverse end surface, with the cornersformed at the intersections of said transverse end surfacewith thesquared side guiding surfaces being removed to form corner surfaces ofsubstantially similar convex cross sections.

10. The T-square defined in claim 9, with the convex surfaces of theblade being polished and buffed to restore the surface tension therein.

References Cited UNITED STATES PATENTS 888,377 5/1908 Wood 33-1891,599,776 9/1926 Lazarevich 3399 3,103,071 9/1963 Dolgorukov 33--112FOREIGN PATENTS 166,893 1/1949 Austria.

990,690 6/ 1951 France.

SAMUEL S. MATTHEWS, Primary Examiner,

7. A T-SQUARE HAVING A HEAD WITH A SQUARED GUIDING SURFACE AND A BLADE HAVING SQUARED SIDE GUIDING SURFACES, THE UPPER SURFACE OF SAID HEAD AND SAID BLADE BEING PERMANENTLY AND UNSEPARABLY CONNECTED TOGETHER FOR THE LIFE OF THE T-SQUARE, THE SIDE GUIDING SURFACES OF SAID BLADE HAVING CONTINUOUS STRAIGHT-LINE EDGES AT THE BOTTOM THEREOF, TWO RECESSES EXTENDING INTO SAID HEAD FROM THE UPPER AND GUIDING SURFACES THEREOF AND HAVING SUBSTANTIALLY UNIFORM DEPTH AND FLAT BOTTOMS PROVIDED ON THE HEAD, AT THE PLACE OF INTERSECTION OF THE GUIDING SURFACE OF THE HEAD WITH THE GUIDING SURFACE OF THE BLADE, A SUBSTANTIAL PART OF EACH RECESS UNDERLYING SAID BLADE AND A SUBSTANTIAL PART OF EACH RECESS BEING EXPOSED BEYOND THE CORRESPONDING GUIDING SURFACE OF SAID BLADE, SAID RECESS HAVING SUCH CONFIGURATION AND SIZE ASA TO RECEIVE THEREIN A SIDE MILLING CUTTER OF AT LEAST 1/16" DIA. IN RECUTTING THE RESPECTIVE SIDE GUIDING SURFACES TO THEIR FULL ORIGINAL LENGTH WITHOUT TOUCHING AN PORTION OF THE HEAD, AND THUS TO PROVIDE FOR REPEAT RECUTTING THE SIDE GUIDING SURFACES WITHOUT DECREASING THE ORIGINAL EFFECTIVE LENGTH THEREOF, WIHTOUT FORMING A STEP WITHIN SUCH LENGTH, AND WITHOUT SEPARATING THE HEAD FROM THE BLADE. 